The present invention relates to a computer-readable medium including a particle data computing program for computing particle data used in simulation which is carried out in a computer, based on a discrete element method (DEM), a particle data computing apparatus that is operated using the program, and a particle data computing method used when the program is executed.
As described in “On Recent Topics about DEM” (Non-patent document 1) which is an article published in “Computational Mechanics” (Vol. 8, No. 3, 2003, pp. 28-33), the DEM is employed when motions of underground particles (or rocks) during a landslide are simulated, or when motions and related circumstances of particles (gravel) around a pipe which has been laid underground are simulated. In the DEM, while numerically integrating an equation of motion with respect to each particle at intervals of a short time step Δt, physical quantities with respect to a motion of each particle are updated. Steps in the DEM are broadly classified into the following three steps of:
1) Contact determination
2) Contact force computation
3) Updating of physical quantities with respect to a motion of each particle using numerical integration
Then, in the DEM, on only a pair of particles determined to be in contact with each other as a result of the contact determination (step 1), the computations (steps 2 and 3) of the contact force and the updating of the physical quantities with respect to the motion of each particle are performed. For this reason, when the process of the contact determination (step 1) is performed at a higher speed, an overall computing speed can be increased. Since the situation that one particle is in contact with another particle or comes away from another particle is changing step by step, it is considered that the contact determination on each particle itself is necessary for each step.
Computation of distances among all the particles in order to perform the contact determination on each particle for each step will become a great burden to the computer, resulting in a significant reduction of the computing speed. However, when the time step Δt is a small value, the motion of each particle within one step is small. For this reason, it can be considered that combinations of a particle which is present in the neighborhood of a focused particle or a particle on which attention is focused but is not in contact with the focused particle, and other particles located in the neighborhood of the focused particle, namely, combinations of contact candidate particle pairs remain almost unchanged. Then, on the grounds that a motion of each particle is small within one step, it is conceived that the contact determination is not performed for several steps and existing contact candidate particle pairs are utilized without alteration. Actually, in order to perform a high-speed operation of the processing, an algorithm as described above is incorporated into some simulation techniques that use the DEM. However, partial omission of the contact determination as described above will lead to computation of a force between particles that are not in contact with each other or failure to compute a contact force between particles actually in contact with each other. Reliability on a result of the simulation may be therefore greatly degraded.